1. Field of the Invention
The present invention relates generally to a surface treatment method for magnesium alloy, and more particularly to an innovative one which features simple treatment process, stable structure and environmental-friendliness in a wide range of applications.
2. Description of Related Art
Due to high activity of magnesium alloy, a loose and porous layer of magnesia is easily formed on its surface, especially in an acid or alkaline environment. So, chemical surface treatment, anodization, vapor deposition process, non-current electroplating or electroplating shall be required to improve the corrosion resistance of magnesium alloy.
With respect to chemical surface treatment, chromate, phosphate or manganate are employed to form a corrosion-resistant metal compound (treatment layer) on the surface of magnesium alloy; but these common toxic solutions and waste liquids will lead to serious environmental pollution.
Moreover, the soft and thin treatment layer subject to chemical treatment can only be taken as an intermediate layer of magnesium alloy, other than a corrosion-resistant surface layer.
If anodization is adopted, the porous and extremely loose magnesium alloy oxiding layer has poorer resistance against corrosion.
The physical or chemical vapor depositions must be conducted under special environmental conditions, but this requires a higher manufacturing cost and strict control while it is difficult to form a thick cladding.
In addition, since magnesium alloy has −2.36V standard reducing potential and higher chemical activity, magnesia (MgO) is easily formed in the atmosphere. Thus, no satisfactory cladding, or even no cladding can be gained by electroplating or non-current electroplating.
If Sn and Zn are electroplated onto the surface of magnesium alloy, the surface is subject to low-temperature heat diffusion (about 190° C.). Sn and Zn can form intermetallic substances such as Mg2Sn with magnesium. However, Sn and Zn must be firstly adhered onto the surface of magnesium alloy by means of electroplating, leading to poorer adhesion of magnesium alloy electroplating layer. Moreover, owing to different reducing potentials of Sn and Zn, the coating of complex alloy is difficult, and multiple electroplating processes also increase the manufacturing process and complexity.
Thus, to overcome the aforementioned problems of the prior art, it would be an advancement if the art to provide an improved structure that can significantly improve the efficacy.
Therefore, the inventor has provided the present invention of practicability after deliberate design and evaluation based on years of experience in the production, development and design of related products.